DOWNSTREAM EVOLUTION OF THE MOST ENERGETIC POD MODES IN THE MIXING LAYER OF A HIGH REYNOLDS NUMBER AXISYMMETRIC JET

摘要

Experimental results were obtained in the potential core region of an ax-isymmetric turbulent jet from 2 to 6 diameters downstream, at Reynolds numbers of 78,400, 117,600, and 156,800. Data were collected using the 138 hot-wire probe used by Citriniti and George (2000). The Proper Orthogonal Decomposition was then applied to a double Fourier transform in time and azimuthal direction of the double velocity correlation tensor. The lowest azimuthal mode for all POD modes, which dominated the dynamics at x/D = 3 in the previous experiments, dies off rapidly downstream. This is consistent with a trend toward homogeneity in the downstream evolution, and suggests that some residual value may control the growth rate of the far jet. On the other hand, for the higher azimuthal modes, the peak shifts to lower mode numbers and actually increases with downstream distance. These mixing layer data, normalized by similarity variables for the mixing layer, collapse at all downstream positions and are nearly independent of Reynolds numbers.